The present invention relates to an improvement in an electric discharge machining apparatus using linear motor drive which supplies a machining power to in a space between an electrode and a workpiece to cause an electric discharge, w and allows the electrode and the workpiece to relatively move by means of a linear motor, thereby machining the workpiece into a desired shape.
FIG. 4 is a configuration view of a conventional electric discharge machining apparatus using linear motor drive-which is disclosed in Japanese Patent Application Laid-open Publication No. 8-309620. In this drawing, the reference numeral 1 denotes an electrode, the reference numeral 2 denotes a workpiece, the reference numeral 3 denotes a spindle head, the reference numeral 4 denotes a chuck, the reference numeral 5 denotes a head, the reference numeral 6 denotes a machining tank, the reference numeral 7 denotes a machining liquid, the reference numeral 8 denotes an X-axis driving linear motor, the reference numeral 9 denotes a Y-axis driving linear motor, and the reference numeral 10 denotes a Z-axis driving linear motor. The electrode 1 is held by the chuck 4 which is connected with the spindle head 3. Further, the workpiece 2 is fixed in the machining tank 6 and dipped in the machining liquid 7. The X-axis driving linear motor 8, the Y-axis driving linear motor 9 and the Z-axis driving linear motor 10 constitutes a driving device which drives the respective axes to cause the electrode 1 and the workpiece 2 move in relation to each other. Additionally, a moving part and a fixed part of each axis driven by the X-axis driving linear motor 8, the Y-axis driving linear motor 9 and the Z-axis driving linear motor 10 are linearly supported by a linear guiding mechanism (not shown) so as to allow relative movement.
The electric discharge machining apparatus using linear motor drive is such that in an electric discharge machining apparatus which supplies an inter-electrode space between the electrode 1 and the workpiece 2 with a machining power by means of a machining power supply unit (not shown), and carries out electric discharge machining on the workpiece 2 to make it into a desired shape, while allowing relative movement of the electrode 1 and the workpiece 2 by means of a driving device, as shown in FIG. 4, a direct driving system by the X-axis driving linear motor 8, the Y-axis driving linear motor 9 and the Z-axis driving linear motor 10 as shown in FIG. 4 is employed.
Such an electric discharge machining apparatus using linear motor drive provides higher positioning accuracy in comparison with those of the type that employs a driving device which involves rotation/longitudinal motion conversion for converting a rotation output of a servo motor to a longitudinal motion by means of a ball screw, because an error such as lead error of ball screw can be eliminated. Furthermore, since there is no power transmission element for carrying out conversion of rotation/longitudinal motion, backlash is eliminated as well as the rigidity is improved, which improves the positioning accuracy and the quick responsibility. Therefore, the electric discharge machining apparatus using linear motor drive can realize high speed and high accuracy electric discharge machining.
FIG. 5 is an explanatory view showing a configuration of a linear motor used in a conventional electric discharge machining apparatus using linear motor drive. In the drawing, the reference numeral 11 denotes a moving part, the reference numeral 12 denotes a fixed part, the reference numeral 13 denotes an iron core, the reference numeral 14 denotes a coil, the reference numeral 15 denotes cooling piping, the reference numeral 16 denotes a magnet, the reference numeral 17 denotes a magnet supporting plate and the reference numeral 18 denotes abase plate, and the moving part 1 which is on the primary side of the linear motor and the fixed part 2 which is on the secondary side of the linear motor are supported by a linear guiding mechanism (not shown) so that they can linearly move in relation to each other. Since the heat generated by the coil 14 can efficiently be cooled by forming the cooling piping in the iron core 13, it is possible to improve the rated characteristics. The configuration described above is disclosed in U.S. Pat. No. 4,839,545, for example.
Because of heat conduction and heat transfer due to heat generation of the driving device of the electric discharge machining apparatus, thermal expansion and thermal distortion will occur in the mechanical structure of the electric discharge machining apparatus. Since machining accuracy on the order of xcexcm is requested for an electric discharge machining apparatus, it is necessary to control these thermal expansion and thermal distortion.
In the conventional electric discharge machining apparatus using linear motor drive having the configurations illustrated in FIGS. 4 and 5, the moving part 11 which is on the primary side of the linear motor is cooled for the purpose of improving rated characteristics of the linear motor, while on the contrary, the fixed part 12 which is on the secondary side of the linear motor is not cooled. In such a conventional electric discharge machining apparatus using linear motor drive, thermal expansion and thermal distortion will occur in the fixed part 12 because of heat transfer from the moving part 11 to the fixed part 12 and dielectric loss of the magnet 16. Therefore, in the electric discharge machining apparatus using linear motor drive in which machining operation proceeds as the electrode 1 and the workpiece 2 move in relation to each other by means of the X-axis driving linear motor 8, the Y-axis driving linear motor 9 and the Z-axis driving linear motor 10 and in which high machining accuracy on the order of xcexcm is requested, the relative positional accuracy of the electrode 1 and the workpiece 2 is deteriorated, which leads the first problem that the machining accuracy of the workpiece 2 decreases.
An electric discharge machining apparatus is often installed in the vicinity of a graphite working machine for machining a graphite electrode, a machining center for performing pre-working on a workpiece and the like, so that usually a lot of dust exists in the vicinity of the electric discharge machining apparatus. Furthermore, volatilization of machining liquid of the electric discharge machining apparatus also occurs.
Moreover, it is difficult to seal the driving parts of the linear motor because they move in the longitudinal direction, and also it is difficult to seal the linear guiding mechanism which supports between the moving part 11 and the fixed part 12 of the linear motor.
Therefore, in the conventional electric discharge machining apparatus using linear motor drive, there arises a second problem that the fixed part 12, the magnet 16 and the moving part 11 of the linear motor get damaged because of the above mentioned dust and volatilization of machining liquid.
The present invention was devised for solving the above mentioned problems. It is an object of the present invention to provide an electric discharge machining apparatus using linear motor drive capable of efficiently conducting cooling operation for preventing thermal expansion and thermal distortion of a mechanical structure due to a rise in temperature of driving parts of linear motor.
It is an another object of this invention to provide an electric discharge machining apparatus using linear motor drive capable of efficiently protecting the driving parts and the like of linear motor from dust.
An electric discharge machining apparatus using linear motor drive according to the present invention is an electric discharge machining apparatus using linear motor drive in which a machining power supply unit supplies a machining power in a space between an electrode and a workpiece and the workpiece is machined while the electrode and the workpiece are moved in relation to each other by means of a driving device implemented by a linear motor. There is provided a cooling device for cooling at least one of a magnet and a magnet supporting plate which supports the magnet which are on the secondary side of the linear motor.
Also, an electric discharge machining apparatus using linear motor drive according to the present invention is an electric discharge machining apparatus using linear motor drive in which a machining power supply unit supplies a machining power in a space between an electrode and a workpiece and the workpiece is machined while the electrode and the workpiece are moved in relation to each other by means of a driving device implemented by a linear motor. There is provided a magnet supporting plate for supporting a magnet which is on the secondary side of the linear motor, a base plate formed with at least one hole portion, a spacer for holding the magnet supporting plate and the base plate while leaving a predetermined space therebetween; and a cooling device for injecting compressed gas from the hole portion of the base plate toward the magnet supporting plate.
Moreover, the magnet supporting plate is formed with a cooling fin.
Furthermore, a dust cover is provided around the driving device configured by the linear motor.
The present invention, which is configured as described above, provides-the following advantage.
The electric discharge machining apparatus using linear motor drive according to the present invention provides an advantage that it is possible to obtain a high-performance and high-accuracy electric discharge machining apparatus using linear motor drive capable of efficiently performing cooling operation for suppressing thermal expansion and thermal distortion of the mechanical structure due to a rise in temperature of the driving parts of linear motor.
Also such an advantage is provided that it is possible to obtain a high-reliability electric discharge machining apparatus using linear motor drive capable of efficiently preventing the driving parts and the like of linear motor from dust.
Also such an advantage is provided that it is possible to achieve the above advantages while suppressing increase of the cost with simple structure.